#include <stdio.h>

int main(void){
    int A;
    long long B, N;
    double x;

    scanf("%d%lld%lld", &A, &B, &N);
    if(B <= N)
        x =  (double)(B - 1)/B;
    else
        x = (double)N/B;
    printf("%d\n", (int)(x*A));
    
    return 0;
}
