#include<stdio.h>
#define mod 1000000007
typedef long long lld;
int n, m, r, a[270], b[270];
lld dy1[270][270], dy2[270][270], dap=1;
void countk(int k){
int i, j;
lld u, d1, d2;
dy1[0][0]=dy2[0][0]=1;
for(i=1; i<=n; i++){
if(b[i]<k)d1=d2=b[i]-a[i]+1, u=0;
else if(a[i]>k)u=b[i]-a[i]+1, d1=d2=0;
else d1=k-a[i]+1, d2=k-a[i], u=b[i]-k;
for(j=0; j<=i; j++){
dy1[i][j] = d1*dy1[i-1][j], dy2[i][j] = d2*dy2[i-1][j];
if(j)dy1[i][j] += u*dy1[i-1][j-1], dy2[i][j] += u*dy2[i-1][j-1];
dy1[i][j] %= mod, dy2[i][j] %= mod;
}
}
dap -= (dy1[n][r-1]-dy2[n][r-1]);
dap %= mod;
if(dap<0)dap += mod;
}
int main(){
int i;
scanf("%d%d", &n, &m);
for(i=1; i<=n; i++)scanf("%d%d", &a[i], &b[i]), dap=dap*(b[i]-a[i]+1)%mod;
scanf("%d", &r);
for(i=0; i<=m; i++)countk(i);
printf("%lld", dap);
return 0;
}
