#include <bits/stdc++.h>

using namespace std;

#define VA_NUM_ARGS(...) VA_NUM_ARGS_IMPL_((0,__VA_ARGS__, 6,5,4,3,2,1))
#define VA_NUM_ARGS_IMPL_(tuple) VA_NUM_ARGS_IMPL tuple
#define VA_NUM_ARGS_IMPL(_0,_1,_2,_3,_4,_5,_6,N,...) N
#define macro_dispatcher(macro, ...) macro_dispatcher_(macro, VA_NUM_ARGS(__VA_ARGS__))
#define macro_dispatcher_(macro, nargs) macro_dispatcher__(macro, nargs)
#define macro_dispatcher__(macro, nargs) macro_dispatcher___(macro, nargs)
#define macro_dispatcher___(macro, nargs) macro ## nargs
#define Debug1(a)           cout<<#a<<"="<<(a)<<"\n"
#define Debug2(a,b)         cout<<#a<<"="<<(a)<<", "<<#b<<"="<<(b)<<"\n"
#define Debug3(a,b,c)       cout<<#a<<"="<<(a)<<", "<<#b<<"="<<(b)<<", "<<#c<<"="<<(c)<<"\n"
#define Debug4(a,b,c,d)     cout<<#a<<"="<<(a)<<", "<<#b<<"="<<(b)<<", "<<#c<<"="<<(c)<<", "<<#d<<"="<<(d)<<"\n"
#define Debug5(a,b,c,d,e)   cout<<#a<<"="<<(a)<<", "<<#b<<"="<<(b)<<", "<<#c<<"="<<(c)<<", "<<#d<<"="<<(d)<<", "<<#e<<"="<<(e)<<"\n"
#define Debug6(a,b,c,d,e,f) cout<<#a<<"="<<(a)<<", "<<#b<<"="<<(b)<<", "<<#c<<"="<<(c)<<", "<<#d<<"="<<(d)<<", "<<#e<<"="<<(e)<<", "<<#f<<"="<<(f)<<"\n"
#define Debug(...) macro_dispatcher(Debug, __VA_ARGS__)(__VA_ARGS__)
#define DA(a,s,n) cout<<#a<<"=["; printarray(a,s,n); cout<<"]\n"

#define TT1 template<class T>
#define TT1T2 template<class T1, class T2>
#define TT1T2T3 template<class T1, class T2, class T3>
template<class T, size_t N> ostream& operator << (ostream& os, const array<T, N>& v);
TT1T2 ostream& operator << (ostream& os, const pair<T1, T2>& p){ return os <<"("<<p.first<<", "<< p.second<<")"; }
TT1 ostream& operator << (ostream& os, const vector<T>& v){       bool f=1;os<<"[";for(auto& i : v) { if (!f)os << ", ";os<<i;f=0;}return os << "]"; }
template<class T, size_t N> ostream& operator << (ostream& os, const array<T, N>& v) {     bool f=1;os<<"[";for(auto& i : v) { if (!f)os << ", ";os<<i;f=0;}return os << "]"; }
TT1T2 ostream& operator << (ostream& os, const set<T1, T2>&v){    bool f=1;os<<"[";for(auto& i : v) { if (!f)os << ", ";os<<i;f=0;}return os << "]"; }
TT1T2 ostream& operator << (ostream& os, const multiset<T1,T2>&v){bool f=1;os<<"[";for(auto& i : v) { if (!f)os << ", ";os<<i;f=0;}return os << "]"; }
TT1T2T3 ostream& operator << (ostream& os, const map<T1,T2,T3>& v){ bool f = 1; os << "["; for (auto& ii : v) { if (!f)os << ", "; os << "(" << ii.first << " -> " << ii.second << ") "; f = 0; }return os << "]"; }
TT1T2 ostream& operator << (ostream& os, const multimap<T1, T2>& v){ bool f = 1; os << "["; for (auto& ii : v) { if (!f)os << ", "; os << "(" << ii.first << " -> " << ii.second << ") "; f = 0; }return os << "]"; }
TT1T2 ostream& operator << (ostream& os, priority_queue<T1, T2> v) { bool f = 1; os << "["; while (!v.empty()) { auto x = v.top(); v.pop(); if (!f) os << ", "; f = 0; os << x; } return os << "]"; }
TT1T2 void printarray(const T1& a, T2 l, T2 r){ for (T2 i = l; i<=r; i++) cout << a[i] << (i<r?" ":""); }

void cio(){
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    cout << setprecision(15);
}

#define tt() printf("%.4f sec\n", (double) clock() / CLOCKS_PER_SEC )

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

#define Fi first
#define Se second
#define pb(x) push_back(x)
#define sz(x) (int)x.size()
#define rep(i, n) for(int i=0;i<n;i++)
#define repp(i, n) for(int i=1;i<=n;i++)
#define all(x) x.begin(), x.end()
#define geti1(X) cin >> X
#define geti2(X,Y) cin >> X >> Y
#define geti3(X,Y,Z) cin >> X >> Y >> Z
#define geti4(X,Y,Z,W) cin >> X >> Y >> Z >> W
#define GET_MACRO(_1,_2,_3,_4,NAME,...) NAME
#define geti(...) GET_MACRO(__VA_ARGS__, geti4, geti3, geti2, geti1) (__VA_ARGS__)

#define endl '\n'

typedef tuple<int,int,int> t3;
typedef tuple<int,int,int,int> t4;
void die(){printf("-1\n"); exit(0);}
int xx[8] = {1,-1,0,0,1,1,-1,-1}, yy[8] = {0,0,1,-1,1,-1,1,-1};
const ll mod = 1e9+9;

int H,W,N;
vector<int> v[200500];
int p[200500];
int main(){
    scanf("%d%d%d",&H,&W,&N);
    repp(i,N){
        int x,y; scanf("%d%d",&x,&y);
        v[y].push_back(x);
    }
    for(int i=1;i<=W;i++) sort(all(v[i]));
    int ans = H;
    p[1] = 1;
    for(int i=2;i<=W;i++){
        p[i] = 1e9;
        int t = p[i-1] + 1;
        if( sz(v[i]) == 0 || v[i][0] > t ){
            p[i] = t; continue;
        }
        bool ok = false;
        for(int j=1;j<sz(v[i]);j++){
            if( v[i][j] <= t ) continue;
            if( v[i][j-1] < t && t < v[i][j] ){
                p[i] = t;
                ok = true;
                break;
            }
            if( v[i][j] - v[i][j-1] > 1  ){
                p[i] = v[i][j-1] + 1;
                ok = true;
                break;
            }
        }
        if( !ok ){
            p[i] = max(t, v[i].back() + 1);
        }
    }
    //repp(i,W) Debug(i, p[i], v[i]);
    for(int i=1;i<=W;i++){
        auto it = lower_bound(all(v[i]), p[i]);
        if( it == v[i].end() ) continue;
        ans = min(ans, *it - 1);
    }
    printf("%d\n",ans);
}



Measured memory_bytes: 9600