//2612468 2011-08-02 20:35:05 Accepted 3167 C 450 160 ylwh!
#include <stdio.h>
#include <string.h>
int main()
{
int n, k, m, i, j;
int ans[1000];
while(scanf("%d%d", &k, &m) != EOF)
{
memset(ans, 0, sizeof(ans));
ans[0] = 1;
n = 0;
while(ans[k-1] != 7)
{
n++;
for(i=0; i<1000; i++)
ans[i] *= m;
for(i=0; i<1000; i++)
{
ans[i+1] += ans[i] / 10;
ans[i] %= 10;
}
}
printf("%d\n", n);
}
return 0;
}