Go: ///
// File:  0528.go
// Author: ymiyamoto
//
// Created on Thu Mar 22 01:52:09 2018
//
package main

import (
	"bufio"
	"fmt"
	"os"
)

var S, T string
var dp [4001][4001]int

func max(a, b int) int {
	if a < b {
		return b
	}
	return a
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	for {
		scanner.Scan()
		S = scanner.Text()
		if len(S) == 0 {
			return
		}

		scanner.Scan()
		T = scanner.Text()

		for i := range dp {
			for j := range dp[i] {
				dp[i][j] = 0
			}
		}

		dp[0][0] = 0
		for i := range S {
			for j := range T {
				if S[i] == T[j] {
					dp[i+1][j+1] = dp[i][j] + 1
				} else {
					dp[i+1][j+1] = 0
				}
			}
		}

		var m int
		for i := range dp {
			for j := range dp[i] {
				m = max(m, dp[i][j])
			}
		}
		fmt.Println(m)
	}
}

C++: #include <cstdio>
#include <cstdint>
#include <cassert>
#include <vector>
#include <algorithm>
#include <string>
#include <set>

template <intmax_t X = 943681729, intmax_t MOD = 1000000007>
class rolling_hash {
  std::vector<intmax_t> hash, offset;

public:
  rolling_hash(const std::string& s): hash(s.length()+1), offset(s.length()+1) {
    for (size_t i = 0; i < s.length(); ++i)
      hash[i+1] = (hash[i]*X+s[i]) % MOD;

    offset[0] = 1;
    for (size_t i = 1; i <= s.length(); ++i)
      offset[i] = offset[i-1] * X % MOD;
  }

  intmax_t get_base() const { return X; }
  intmax_t get_mod() const { return MOD; }

  intmax_t prefix(size_t i) const {
    // hash of prefix s[0..i-1] (inclusive)
    assert(0 < i);
    return hash[i];
  }

  intmax_t substr(size_t i, size_t j) const {
    // hash of substring s[i..j-1] (inclusive)
    assert(i < j);
    intmax_t res = hash[j];
    res = (res - offset[j-i]*hash[i]) % MOD;
    if (res < 0) res += MOD;
    return res;
  }

  intmax_t inserted(size_t i, int ch) const {
    intmax_t res = 0;
    if (i > 0) res += prefix(i);
    res = (res*X + ch) % MOD;
    size_t n = hash.size()-1;
    if (i < n) res = (res*offset[n-i] + substr(i, n)) % MOD;
    return res;
  }

  void debug() const {
    for (size_t i = 0; i < hash.size(); ++i)
      fprintf(stderr, "%jd%c", hash[i], i+1<hash.size()? ' ':'\n');
  }
};

int testcase_ends() {
  char buf[4096];
  if (scanf("%s", buf) == EOF) return 1;
  std::string s = buf;
  scanf("%s", buf);
  std::string t = buf;

  size_t n = s.length();
  size_t m = t.length();

  rolling_hash<> rs(s), rt(t);

  std::set<intmax_t> rl;
  for (size_t i = 0; i < n; ++i)
    for (size_t j = i+1; j <= n; ++j)
      rl.insert(rs.substr(i, j));

  size_t res = 0;
  for (size_t i = 0; i < m; ++i)
    for (size_t j = i+1; j <= m; ++j)
      if (rl.count(rt.substr(i, j)))
        res = std::max(res, j-i);

  printf("%zu\n", res);
  return 0;
}

int main() {
  while (!testcase_ends()) {}
}

C++: #include<iostream>
#include<cstring>
#include<string>

using namespace std;

int main(void){
	int a,b;
	string str;
	string str2;
	while(cin >> str >> str2){
		int ans=0;
		for(a=0;a<str.size();a++){
			int res=0;
			string tmp= str.substr(a, str.size()-a);
			for(b=0;b<min(tmp.size(),str2.size());b++){
				if(tmp[b]==str2[b])res++;
				else ans=max(res,ans),res=0;
				if(min(tmp.size(),str2.size())-1==b)ans=max(res,ans);
			}
		}
		cout << ans << endl;
	}
	return 0;
}

C++: #include "iostream"
#include "climits"
#include "list"
#include "queue"
#include "stack"
#include "set"
#include "functional"
#include "algorithm"
#include "string"
#include "map"
#include "unordered_map"
#include "unordered_set"
#include "iomanip"
#include "cmath"
#include "random"
#include "bitset"
#include "cstdio"
#include "numeric"
#include "cassert"

using namespace std;

const long long int MOD = 1000000007;
//const int MOD = 1000000007;
//const int MOD = 998244353;

long long int N, M, K, H, W, L, R;
//int N, M, K, H, W, L, R;

int main() {
	//ios::sync_with_stdio(false);
	//cin.tie(0);

	string s, t;
	while(cin>>s){
	    cin>>t;
	vector<vector<int>>dp(s.size() + 1, vector<int>(t.size() + 1));
	for (int i = s.size() - 1; i >= 0; i--) {
		for (int j = t.size() - 1; j >= 0; j--) {
			if (s[i] == t[j])dp[i][j] = dp[i + 1][j + 1] + 1;
		}
	}
	int ans = 0;
	for (auto i : dp)for (auto j : i)ans = max(ans, j);
	cout << ans << endl;
	}
	return 0;
}

C++: #include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
char str1[4000], str2[4000];
int main() {
    while (scanf("%s%s",&str1,&str2)!=EOF) {
        int res=0;
        for (int off=-1*(int)strlen(str1); off<=(int)strlen(str2); off++) {
            int len=0;
            for (int i=max(off,0); i<min(strlen(str1)+off,strlen(str2)); i++) {
                if (len>res) res=len;
                if (str1[i-off]!=str2[i]) len=0;
                else len++;
            }
        }
        printf("%d\n",res);
    }
}

C++: #include<iostream>
#include<algorithm>
#include<vector>
#include<stack>
#include<map>
#include<set>
#include<queue>
#include<cstdio>
#include<climits>
#include<cmath>
#include<cstring>
#include<string>
#include<sstream>
#include<numeric>
#include<cassert>

#define f first
#define s second
#define mp make_pair

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,c) for(__typeof((c).begin()) i=(c).begin(); i!=(c).end(); i++)
#define ALL(c) (c).begin(), (c).end()
#define IN(x,s,g) ((x) >= (s) && (x) < (g))
#define ISIN(x,y,w,h) (IN((x),0,(w)) && IN((y),0,(h)))
#define print(x) printf("%d\n",x);

using namespace std;

typedef unsigned int uint;
typedef long long ll;

const int _dx[] = {0,1,0,-1};
const int _dy[] = {-1,0,1,0};

int getInt(){
  int ret = 0,c;
  c = getchar();
  while(!isdigit(c)) c = getchar();
  while(isdigit(c)){
    ret *= 10;
    ret += c - '0';
    c = getchar();
  }
  return ret;
}

char str1[4010];
char str2[4010];

int main(){
  while(~scanf("%s %s",str1,str2)){
    int ans = 0;
    for(int i=0; str1[i]; i++){
      for(int j=0; str2[j]; j++){
        if(str1[i] == str2[j]){
          int tmp = 0;
          int ii = i;
          int jj = j;
          while(str1[ii] && str1[ii++] == str2[jj++])
            ++tmp;
          ans = max(ans, tmp);
        }
      }
    }
    print(ans);
  }
  return 0;
}