#include <stdio.h>

int main()
{
long sum;
int i,g,w,e[1001],c[1001];
freopen("energii.in","r",stdin);
freopen("energii.out", "w", stdout);
scanf("%d", &g);
scanf("%d", &w);

for(i=1;i<=g;i++) scanf("%d %d", &e[i], &c[i]);

sum=0;
for (i=1;i<=g;i++) sum+=e[i];
if (sum<w) printf("-1");
if (sum==w) {
sum=0;
for(int i=1;i<=g;i++) sum+=c[i];
printf("%ld",sum);
}

return 0;
}