#include <stdio.h>

int main(void) {
    unsigned long long int A = 0;
    unsigned long long int B = 0;
    unsigned long long int N = 0;
    unsigned long long int max = 0;
    scanf("%lu %lu %lu", &A, &B, &N);
    for (int x = 0;x <= N; x++) {
        if (max < (A * x / B - A * (x / B))) {
            max = (A * x / B - A * (x / B));
        }
    }
    printf("%lu", max);
    return 0;
}