"use strict";
    
const main = arg => {
    arg = arg.trim().split("\n");
    const A = parseInt(arg[0].split(" ")[0]);
    const B = parseInt(arg[0].split(" ")[1]);
    const N = parseInt(arg[0].split(" ")[2]);
    
    let answer = 0;
    
    if(B - 1 < N) {
        answer = Math.floor((A * (B-1)) / B) - (A * Math.floor((B-1) / B));
    } else {
        answer = Math.floor((A * N) / B) - (A * Math.floor(N / B));
    }
    
    console.log(answer);
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));
