#include <iostream>
#include <math.h>
using namespace std;
int x,h,m;
void goback(){
    if(m==0 & h==0){
        h=23;
        m=59;}
    else if(m==0){
        h--;
        m=59;
    }
    else
        m--;
}
bool check(int m,int h){
    bool test = false;
    int c;
    while(m!=0){
        c = m % 10;
        m = m / 10;
        if(c==7){
            return true;
            break;
        }
    }
    while(h!=0){
        c = h % 10;
        h = h / 10;
        if(c==7){
            return true;
            break;
        }
    }
    return test;
}
int main(){


    cin>>x;
    cin>>h;
    cin>>m;
    int total=0;
    while(check(m,h)==false){
    goback();
    total++;
    }
    int y = total/x;
    cout<<y;;
}