Problem:
Score: 400 points

Problem Statement

Amidakuji is a traditional method of lottery in Japan.

To make an amidakuji, we first draw W parallel vertical lines, and then draw horizontal lines that connect them. The length of each vertical line is H+1 [cm], and the endpoints of the horizontal lines must be at 1, 2, 3, ..., or H [cm] from the top of a vertical line.

A valid amidakuji is an amidakuji that satisfies the following conditions:

No two horizontal lines share an endpoint.

The two endpoints of each horizontal lines must be at the same height.

A horizontal line must connect adjacent vertical lines.

Find the number of the valid amidakuji that satisfy the following condition, modulo 1\ 000\ 000\ 007: if we trace the path from the top of the leftmost vertical line to the bottom, always following horizontal lines when we encounter them, we reach the bottom of the K-th vertical line from the left.

For example, in the following amidakuji, we will reach the bottom of the fourth vertical line from the left.

Constraints

H is an integer between 1 and 100 (inclusive).

W is an integer between 1 and 8 (inclusive).

K is an integer between 1 and W (inclusive).

Input

Input is given from Standard Input in the following format:

H W K

Output

Print the number of the amidakuji that satisfy the condition, modulo 1\ 000\ 000\ 007.

Sample Input 1

1 3 2

Sample Output 1

1

Only the following one amidakuji satisfies the condition:

Sample Input 2

1 3 1

Sample Output 2

2

Only the following two amidakuji satisfy the condition:

Sample Input 3

2 3 3

Sample Output 3

1

Only the following one amidakuji satisfies the condition:

Sample Input 4

2 3 1

Sample Output 4

5

Only the following five amidakuji satisfy the condition:

Sample Input 5

7 1 1

Sample Output 5

1

As there is only one vertical line, we cannot draw any horizontal lines. Thus, there is only one amidakuji that satisfies the condition: the amidakuji with no horizontal lines.

Sample Input 6

15 8 5

Sample Output 6

437760187

Be sure to print the answer modulo 1\ 000\ 000\ 007.

Solution in C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
long int pow2(int s){
    int t=1;
    for(int i=0;i<s;i++){
        t=t*2;
    }
    return t;
}
long int move(int h,int w,int k,int W1,int Amida[][W1]){
    long int c=0;
    int x=0,y=1;
    for(int i=0;i<h+1;i++){
        if(x==0 && Amida[y][x+1]==1){
            x=x+2;
            y++;
        }else if(x==0 && Amida[y][x+1]!=1 ){
            y++;
        }else if(x!=0 && x!=W1-1 && Amida[y][x+1]==1){
            x=x+2;
            y++;
        }else if(x!=0 && x!=W1-1 && Amida[y][x-1]==1){
            x=x-2;
            y++;
        }else if(x!=0 && x!=W1-1 && (Amida[y][x-1]!=1 && Amida[y][x+1]!=1)){
            y++;
        }else if(x==W1-1 && Amida[y][x-1]==1){
            x=x-2;
            y++;
        }else if(x==W1-1 && Amida[y][x-1]!=1){
            y++;
        }
        if(y==h+1)break;
    }
    if(x==(2*k-2) && y==h+1)c++;
                 return c;
}

                 
int main(void){
    
    long int C=0,R,f=0;
    int H,K,o;
    int W;
    scanf("%d",&H);scanf("%d",&W);scanf("%d",&K);
    int W1=2*W-1;
    int Amida[H+2][W1];
    for(int i=0;i<H+2;i++){
        for(int j=0;j<W1;j++){
            Amida[i][j]=0;
        }
    }
    int q=move(H,W,K,W1,Amida);
    C=C+q;
    for(long int m=2;m<=pow2((H)*(W-1));m++){
                    for(int i=1;i<W1;i=i+2){
                        for(int j=1;j<=H;j++){
                            R=pow2(H*(i/2)+j-1);
                            if((m-1)%R==0){
                                if(Amida[j][i]==1){
                                    Amida[j][i]=0;
                                }else if(Amida[j][i]==0){
                                    Amida[j][i]=1;
                                }
                            }
                        }
                    }
        f=0;
        for(int i=1;i<=H;i++){
            for(int j=1;j<W1-2;j=j+2){
                if((Amida[i][j]+Amida[i][j+2])==2){f++;}
            }

        }
        if(f==0){
            o=move(H,W,K,W1,Amida);
            C=C+o;
        }
                }
    long int x=C%1000000007;
                printf("%ld\n",x);
                return 0;
        }